So I have a technics SL1200 turntable with a busted driver board. The motor spins but it will only move forwards and backwards and not turn. The problem is traced to various IC on the board that are no longer made and replacement chips cost as much as a 10th gen core i7.
I'm thinking of just removing the entire board, retain the motor which is attached to the driver board, and use a generic bldc motor driver and an Arduino to get it to spin at exactly 33.3 rpm, then figure out how to wire the buttons on the turntable to do what it says, such as start, stop, 33 rpm, 45 rpm, pitch shift (it varies the rpm), and all that.
Basically emulate the drive on the turntable.
Anyone done anything like this? Motor is like maybe 14 watts so it won't be anything big.
Are you sure that the original motor is a BLDC-motor? I am far away from beeing an expert about turntables but I would be very astonished if this motor is a brushless-motor.
Is there a big gear reduction between motor and turntable?
BLDCs use to run at high rpms
This turntable is direct drive, most technics turntable is in fact direct drive, and there are no brushes. Google the picture if their internals and you'll know what I mean. The platter contains a permanent magnet ring, while the stator is on the motherboard with a bunch of coils that energize in sync to spin it.
But they use ics such as the AN6680 and 6685 which is no longer made and I have no other way to fix this table, except to find some other way to drive the motor and issue commands to it.
I think that is going to be a long hard road, unless Technics are willing to provide specs for their custom chips (which seems unlikely). Since the chips were discontinued about 5 years ago, a lot of people face similar problem, but apart from getting replacement chips it does not appear anyone has found an alternative. I have seen the AN6680 on sale for $130, that would would seem a more viable option.
Tbh, I think you have to mourn the loss, then move on to something new.
I heard that technics is producing the turntable again, so are they using existing stocks of their chips or are they using something else? If need be I can just gut the internals and put new motor in them.
All were talking about is to just spin the platter at 33 rpm, plenty of servo or stepper motors can do it.
Do they not make standard servo motor and driver sets?
And yes service manuals with schematic are out there.
I'm thinking the fact that the platter moves at all means the drive system works, but whatever is telling them where and how fast to spin is broken. If I can only figure out where, I could fix it.
Otherwise I'm thinking just a servo or stepper motor and driver, and program the Arduino to spin them at 33.3 rpm when the 33rpm switch is pressed, and 45 rpm when 45 rpm switch is pressed. The strobe led can be programmed to flash at whatever they are supposed to flash, and the pitch control can be wired to the Arduino that tells it to vary the rpm.
Turntable had mechanical problems but I fixed it, but I'm not an electronic engineer, just mechanical.
I'm told by the person who owns the deck that it had been water damaged. I'm not seeing any evidence of corrosion or anything in the internals, they look fine to me. Basically he stored a bunch of records in a basement and a typhoon flooded it. So he has a bunch of records without sleeves for this reason, they all got water damaged. Some don't even have a label so no idea what they even are.
If the turntable oscillates its probably a fault in the controller chip AN6680.
Technics made custom ICs for these turntables, that tells you it is not "just a simple servo motor".
If you want to rip out the Technics motor and stick in a cheap stepper motor and get very poor audio quality then I guess you can do that. Depends on whether the goal is to reproduce the original Technics audio quality, or have essentially a DIY project housed in a Technics box.
So does the an 6680 controller drive the motor, or issues commands, or both?
I've measured the voltage as outlined in the service manual of the various pins on the an6680 and they are all within spec, however ic 302 (I don't remember the model number, sv something) has really high voltage coming off some of the legs. I'm suspecting that one.
I'm looking at schematics for a 1200MK2.
The 6680 is some kind of phase locked loop IC that controls the speed.
The 6675 is the servo motor driver IC, some high voltages on it may be normal.
It's going to be impossible for me to help you debug via these little chat sessions.
You should go to one of Audiophile forums for help.
Replacing the entire guts with a new motor and some kind of Arduino controller may not be practical
Why would they know anything about electrical engineering or motor controls? All they know is expensive snake oil audio cable costing 2000 dollars...
Besides they'll just say "replace that chip" except it's a chip that costs more than freaking Intel Core i7's and does not even exist except to take it from another turntable.
That IC is for the pitch control. You probably could eliminate it and generate the pitch control signal with an Arduino.
However, the 9V for that IC comes from a transistor and a regulator inside the 6680 so it is probably also bad.